Developer Guide: git setup and workflow

[rcomer]

See #2963, where the removal of these two sections was agreed.

In the Development Workflow, I have added a link to the Pull Request Checklist between the editing instructions and the "submitting for review" instructions. This is because I completely failed to notice the PR checklist before I submitted my first PR!

[rcomer]

I've not seen this one from Travis before

No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received

The build has been terminated

[ajdawson]

All good now, thanks @rcomer.